A transmission for a vehicle acts as a torque and speed changer by providing suitable gear ratio changes that enable the engine to propel the vehicle under various loads. There are three basic types of transmissions for vehicles: a manual transmission in which the driver directly controls the shifting of gears, an automatic transmission which automatically shifts gears according to road load and throttle opening, and a continuously variable transmission in which speeds are continuously shifted over the entire spectrum of speeds without steps therebetween.
The present invention is related to the continuously variable transmission which offers many advantages over the conventional automatic transmission using including decreased fuel consumption and overall weight, and improved power transmission performance.
Continuously variable transmissions generally use two pulleys mounted respectively on input and output shafts. A diameter of each pulley is variable, and the pulleys are connected to each other by a steel belt or chain. Shift ranges of the transmission are continuously varied through the changes in diameter of the pulleys.
However, continuously variable transmissions using only a belt connecting diameter-variable pulleys have a drawback in that they are limited in the scope of shift ranges available. As a result, engine power is not effectively utilized.
Further, because all rotational power is transmitted through a single belt, the belt can become quickly worn, reducing the life span of the belt.